Virtual stereographic display system

ABSTRACT

A virtual stereographic display system which includes a display image surface, a polarizer disposed before the display image surface, a liquid crystal cell in which ferroelectric smectic liquid crystal is aligned, and disposed before the polarizer, a driving circuit connected to the liquid crystal cell so as to apply AC voltage synchronized with the frame signal of the image on the display image surface to the liquid crystal cell and to switch over the, polarization axes of the display light proceeding from the display image surface through the polarizer and liquid crystal cell by time division, and polarizing glasses having different polarization axes for the left eye and right eye for viewing the display light.

BACKGROUND OF THE INVENTION

The present invention generally relates to an image display arrangementand more particularly, to a stereographic image display system such as astereoscopic television or the like which utilizes parallax between theleft and right eyes.

Various attempts have been made since very old times to realizethree-dimensional images or stereographic images, and there are a largenumber of systems available therefor at present including laserhologram, etc. However, the systems that are successfully put intoactual application as stereographic image display arrangements arecurrently limited to the following two systems. Each of these systems isbased on a principle in which images for left and right eyes areseparately displayed so as to bring about a false impression ofstereoscope, or hallucinate viewers as if there were parallax due to astereographic or solid object, based on the deviation between individualimages composed on the retinas of a viewer's eyes, thereby effecting avirtual stereographic display of images.

The two systems referred to above are:

(1) The system in which images for left and right eyes are formed byplane-polarized light so that the polarization axes thereof are directedto form an angle of 90° with respect to each other, and thus, the imagesare observed in a separated state by glasses with polarizing plates.This system is mainly adopted in stereoscopic movies for theaters.

(2) The system in which images for left and right eyes are alternatelydisplayed through time division by alternately switching the opening orof the glasses that function by an electronic light valve, insynchronization with the period of display, and the intendedstereographic image display is effected.

The system in item (1) is close to ideal, since the stereographic imagesobtained thereby are free from flickering, while the glasses withpolarizing plates to be worn by the viewers are light and inexpensive.However, in this known system, two display devices and projectingdevices are required in order to simultaneously project two images withdifferent polarization axes at all times, thus resulting in an increaseof the number of devices involved, with a consequent complication ofoperations, and therefore, this system is not suitable for domestic usein general.

On the other hand, in the system referred to in item (2), although someflickering is noticed due to the half reduction of the number of framesper second which enters the left and right eyes, the system is realisticin that the stereographic image can be formed by one television set.

With respect to the system in item (2), a virtual stereographic displayarrangement has conventionally, as utilizing a television set, a systemin which glasses having an electronic light valve function areconstituted by liquid crystal cells, thereby switching the glasses withthe light valve function for opening or closing in synchronization withthe frame frequency or the field frequency of the television set.

However, the above known system also has a problem in that each of theviewers must inevitably wear the glasses with the electronic light valvefunction. More specifically, such glasses are not only heavy and causefatigue after wearing them for a long time, but such glasses also tendto be expensive due to provision of the light valve function, and the,cost therefor becomes a considerable amount when they are purchased fora number of viewers.

Moreover, most of the glasses with the electronic light valve functiontend to eye give rise to fatigue due to the fact that the intensity ofthe transmitted light largely varies following the opening or closing ofthe light valves. Meanwhile, in the practice which utilizes a polarizedlight, it is unavoidable to reduce the intensity of the transmittedlight to less than half based on the principles of polarized light, witha consequent defect that the displayed images appear to be dark. a lightvalve device which removes such a defect has also been proposed whichutilizes dynmaic-scattering mode (DSM) of nematic liquid crystal, butsuch a device cannot fully cope with the frame frequency for the imagedisplay, since the dynamic-scattering mode has a slow response speed.

Furthermore, in the system of item (2), it is necessary to have theopen/close function of the electronically controlled light valvessynchronized with the display of images for the left and right eyesrespectively, and conventionally, the signal has been derived from thevertical synchronizing signal of the television circuit. However, if theabove practice is to be applied to an existing television set, it isrequired either to remodel internal circuits of the television set or toseparately provide an adapter with a tuner only for deriving thesynchronizing signal. Such remodeling is very difficult to be made athome in general, while the adapter with a tuner is a considerableexpense for the user to purchase.

Generally, in the conventional virtual stereographic or stereoscopicdisplay system utilizing the television set as described above, sincethe number of frames per second which enters each of the left and righteyes following open/close functions of the light valves of the glassesis to be reduced to half as compared with that in the normal display,flickering is noticed which results in eye fatigue. In order toeliminate such a disadvantage, there has been proposed a practice toincrease the number of frames per second for the display, but alterationof a standard for the frame frequency makes it difficult to maintaininterchangeability with respect to existing devices, and is notconsidered to be practical.

SUMMARY OF THE INVENTION

Accordingly, an essential object of the present invention is to providea virtual stereographic display system of multiplexed double image typewhich is suitable for viewing by many persons, e.g., at home in generalor in classrooms, etc.

Another important object of the present invention is to provide avirtual stereographic display system of the type described above whichis equipped with observation glasses having an electronic light valvefunction with less eye fatigue, and a driving device for such glasses.

A further object of the present invention is to provide a virtualstereographic display system which is provided with a function capableof readily generating a synchronizing signal for driving the lightvalves at low cost, without the necessity of remodeling an existingtelevision set.

Still another object of the present invention is to provide a virtualstereographic display system capable of reducing eye fatigue due toflickering, without increasing the frame frequency.

The present invention intends to solve, as described below, the problemsreferred to above and those taking place in the virtual stereographicdisplay system in which image information for the right eye and the lefteye is alternately displayed on a television screen, and light signalsof the image information are observed by wearing glasses having a pairof light valves to be alternately opened or closed in synchronizationwith the switching-over cycle of the image information for the right andleft eyes.

In the first place, for solving the problem of glasses to be worn by theviewer with an electronic light valve function that tend to be heavy andexpensive, the present inventors have presented a practice in which apolarization control panel utilizing a ferroelectric liquid crystal ofbirefringence type or guest-host type is disposed in front of thescreen, and by observing panel through glasses with polarizes, the imageinformation is discriminated by the left and right eyes.

Then, as means for reducing the fatigue of eyes due to rapid variationsin the intensity of the transmitted light following the opening orclosing of valves, a practice has been proposed to observe the imagesthrough glasses equipped with light valves of transient-scattering modeof ferroelectric liquid crystal cells.

Meanwhile, as means for generating the synchronizing signal at low costthrough utilization of video equipment such as an existing televisionset, etc., the present inventors have developed a novel means by whichthe brightness variation on the image screen is converted intoelectrical signals by a photo-sensor so as to be subjected frequencydivision and phase adjustment, thereby to producing the synchronizingsignal.

Finally, the unit for eliminating the undesirable flickering throughlowering of the frame frequency is characterized in that the unit forswitching-over the two kinds of image information for the right and lefteyes is constituted by one scanning line or a group of a predeterminedplurality of scanning lines. It is to be noted here that the unit forconstituting the image is limited to one that utilizes the scanning linein the present invention.

It is also to be noted here that, according to the present invention,although the open/close cycle of the light valves is of a high speed at15.75 KHz, e.g., in the NTSC system, the present inventors havecompleted the present invention by making it possible to effect theopen/close function at such a high speed through utilization of, forexample, the birefringence effect of the ferroelectric liquid crystalfor light valves. However, the light valves to be employed in thepresent invention are not limited to those which employ theferroelectric liquid crystal.

The term "television" referred to in the present specification relatesto the arrangement adapted to transmit images as converted intoelectrical signals via passages through a wire or wireless system forreproduction of the images by a receiving set. The display device to beused may be the CRT (cathode ray tube), liquid crystal display unit,electro-luminescence display, light emitting diode matrix display,plasma display and screen of a projecting type television, etc. In thepresent invention, except for those utilizing the scanning lines, allarrangements may be applicable also to video equipment employing films.

In accomplishing the above objects and other objects, according to onepreferred embodiment of the present invention, a virtual stereographicdisplay system is provided. The system includes a display image surface,a polarizer disposed before the display image surface, a liquid crystalcell in which ferroelectric smectic liquid crystal is aligned anddisposed before the polarizer, a driving circuit connected to the liquidcrystal cell so as to apply AC voltage synchronized with frame signal ofthe image of the display image surface to the liquid crystal cell and toswitch over by time division the polarization axes of display lightproceeding from the display image surface through the polarizer and theliquid crystal cell, and polarizing glasses having differentpolarization axes for the left and right eye for viewing the displaylight.

Since the stereographic display system of the multiplexed double imagetype according to the present invention has such advantages that thearrangement is simple in construction, and moreover, the glasses to beworn by the viewers are light and inexpensive, the system may be readilyutilized at home in general and in classrooms, etc., thus being verysuitable for actual applications.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome apparent from the following description taken in conjunction withthe preferred embodiments thereof with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram showing a virtual stereographic displaysystem according to one preferred embodiment of the present invention;

FIG. 2 is a diagram similar to FIG. 1, which particularly shows amodification thereof;

FIGS. 3(A) to 3(C) are explanatory diagrams of angular configurations ofoptical axes and polarizing axes for optical systems shown in FIGS. 1and 2;

FIGS. 4(A), 4(B), 5(A) and 5(B) are diagrams for explaining thefunctioning principles of liquid crystal cells to be employed in theembodiment of the present invention;

FIG. 6 is a diagram for explaining memory effect of the liquid crystalcell to be employed in the embodiment of the present invention;

FIG. 7 shows one example of a voltage waveform to be applied to theliquid crystal cell;

FIG. 8 is a schematic diagram showing a virtual stereographic displaysystem according to a second embodiment of the present invention;

FIG. 9 is a diagram for explaining angular configurations of a liquidcrystal cell and a quarter-wave plate for the optical system of FIG. 8;

FIG. 10 is a schematic diagram for a virtual stereographic displaysystem showing a modification of the arrangement of FIG. 8;

FIG. 11 is a diagram for explaining the angular configuration in themodification of FIG. 10;

FIGS. 12(A), 12(B), 13(A) and 13(B) are diagrams for explaining thefunctioning principles of the liquid crystal cells to be employed in theembodiment of the present invention;

FIG. 14 is a schematic diagram for a virtual stereographic displaysystem according to a third embodiment of the present invention;

FIG. 15 is a schematic cross section of a liquid crystal cell to beemployed in the glasses shown in FIG. 14;

FIGS. 16(A) to 16(D) are diagrams that are used for explaining thefunctioning principles of the liquid crystal cell employed in theglasses of FIG. 14;

FIG. 17 is a graph for explaining the electro-optical effect of theliquid crystal cell employed in the glasses of FIG. 14;

FIG. 18 is a waveform diagram showing one example of a voltage waveformto be applied to the liquid crystal cell employed in the glasses of FIG.14;

FIG. 19 is a schematic diagram showing a virtual stereographic displaysystem according to a fourth embodiment of the present invention;

FIG. 20 is a diagram similar to FIG. 19, which particularly shows amodification thereof;

FIGS. 21(A) to 21(F) are waveform diagrams for explaining the process ofobtaining a synchronizing signal for driving the light valves, based onthe brightness signal of the image display surface;

FIGS. 22(A) to 22(C) are diagrams for explaining the state of scanninglines on the image display surface;

FIGS. 23(A) to 23(E) are diagrams for explaining the synchronzingrelation in the open/close functions for the television signal sent tothe image display surface and the glasses with light valves; and

FIG. 24 is a schematic diagram showing a virtual stereographic displaysystem according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the description of the present invention proceeds, it is to benoted that like parts are designated by like reference numeralsthroughout the accompanying drawings.

In the first place, it is to be noted that the display system accordingto one preferred embodiment of the present invention is characterized inthat the stereographic image display is effected in such a manner that,with a liquid crystal cell disposed before a television image surface,the polarization axis of light travelling through said liquid crystalcell is alternately switched over by time division for observation byglasses with polarizing plates through separation into left and righteyes.

[FIRST EMBODIMENT]

Referring now to the drawings, there is shown in FIG. 1 a generalconstruction of a virtual stereographic or stereoscopic image displaysystem V1 according to one preferred embodiment of the presentinvention. The system generally includes an image display surface 101,e.g., of a television set T, a polarizer or polarizing panel 102disposed before the image display surface 101, and a liquid crystal cell103 further disposed before said polarizer 102, with a driving circuit104 for driving the liquid crystal cell 103 that is connected betweenthe television set and the liquid crystal cell 103 as illustrated.

The liquid crystal cell 103 is prepared through a homogeneous alignmentof the ferroelectric smectic liquid crystal, and the cell is providedwith transparent electrodes (not particularly shown) disposed at theinner sides of its substrates between which the liquid crystal isenclosed. In this system, the liquid crystal cell 103 functions as anoptical compensator capable of rotating the optical axis within theplane of the cell by inverting the polarity of the applied voltage. Thedriving circuit 104 for the liquid crystal cell 103 is intended to forma voltage waveform to be applied to the liquid crystal cell 103, andarranged to alternately switch-over the optical axis of the liquidcrystal cell 103 in synchronization with the frame signal of thetelevision signal fed from the television set T. Observation glasses105, provided for a viewer to wear, are equipped with polarizing plateshaving different polarization axes respectively for the left and righteyes. By alternately changing over the polarization axes of light of thetelevision images for observation by the glasses with the polarizingplates in a separated manner at the left and right eyes through timedivision, the left and right eyes individually watch the televisionimages, and in this case, the television images are observed by the leftand right eyes with a stereoscopic parallax.

Depending on the way for utilizing the polarized light, the arrangementof FIG. 1 may be so modified as in a display system V1B in FIG. 2, inwhich a quarter-wave plate 106 is further disposed before the liquidcrystal cell 103 so as to convert a plane-polarized light travellingthrough said cell 103 approximately in a circularly polarized light.

For introducing the fundamental constructions in FIGS. 1 and 2 intoactual applications, there may be conceived three typical systems asdescribed below according to the kinds of polarization and retardationof the crystal cell 103.

In a first system, circularly polarizing plates or polarizers areemployed for the glasses 105 in the arrangement of FIG. 1. For theliquid crystal cell 103, a liquid crystal cell may be employed havingretardation in the range of 0.1 to 0.15 micron, and rotational angles ofthe optical axis due to polarity inversion of the applied voltage, inthe range of 70° to 110°. Since the liquid crystal cell 103 is adaptedto function as a quarter-wave plate, a cell with the retardation of 0.13micron and rotation angle of the optical axis at 90° is particularlypreferable.

For the disposition of the liquid crystal cell 103 and the polarizer102, a setting is made as shown in FIG. 3(A), so that a middle line oftwo optical axes 202 and 203 may be taken by the optical axis of theliquid crystal cell 103 which is aligned or generally aligned with thepolarizing axis 201 of the polarizer 102. The light of the televisionimages becomes the circularly polarized light by the polarizer 102 andthe liquid crystal cell 103, and its polarizing axis may be alternatelyswitched over to the left or right through polarity inversion of thevoltage to be applied to the liquid crystal cell 103.

In a second system, plane-polarizing plates or polarizers are employedfor the glasses 105 in the arrangement of FIG. 1. For the liquid crystalcell 103, a liquid crystal cell may be employed having retardation inthe range of 0.2 to 0.3 micron, and rotational angles of the opticalaxis due to polarity inversion of the applied voltage, in the range of35° to 55°. Since the liquid crystal cell 103 is adapted to function asa half-wave plate, a cell with the retardation of 0.25 micron androtational angle of the optical axis at 45° is particularly preferable.

For the disposition of the liquid crystal cell 103 and the polarizer102, a setting is made as shown in FIG. 3(B), so that one of two opticalaxes 202 and 203 may be taken by the optical axis of the liquid crystalcell 103 which is aligned or generally aligned with the polarizing axis201 of the polarizer 102. The light of the television images becomes theplane-polarized light by the polarizer 102 and the liquid crystal cell103, and its polarizing axis may be alternately switched over in twodirections intersecting at right angles through polarity inversion ofthe voltage to be applied to the liquid crystal cell 103. In the angularconfiguration of the polarizing axes 204 and 205 of the twoplane-polarizing plates to be attached to the glasses 105, it is soarranged that one is aligned with the polarization axis of the polarizer102 at the side of the television image surface, while the other is setat an angle for intersection at right angles therewith.

In a third system, circularly polarizing plates or polarizers areemployed for the glasses 105 in the arrangement of FIG. 2. For theliquid crystal cell 103, a liquid crystal cell may be employed havingretardation in the range of 0.2 to 0.3 micron, and rotational angles ofthe optical axis due to polarity inversion of the applied voltage, inthe range of 35° to 55°. Since the liquid crystal cell 103 is adapted tofunction as a half-wave plate, a cell with the retardation of 0.25micron and rotational angle of the optical axis at 45° is particularlypreferable.

For the disposition of the liquid crystal cell 103 and the polarizer102, a setting is made as shown in FIG. 3(C), so that one of two opticalaxes 202 and 203 may be taken by the optical axis of the liquid crystalcell 103 which is aligned or generally aligned with the polarizing axis201 of the polarizer 102. The optical axis 206 of the quarter-wave plate106 is so set as to form an angle of approximately 45° with respect tothe polarizing axis of the polarizer 102. The light of the televisionimages becomes the circularly-polarized light by the polarizer 102, theliquid crystal cell 103, and the quarter-wave plate 106, and itspolarizing axis may be alternately switched over toward the left orright through polarity inversion of the voltage to be applied to theliquid crystal cell 103.

In the three systems described in detail so far, the retardation of theliquid crystal cell 103, rotational angle or angular configuration ofthe optical axis, retardation of the quarter-wave plate 106, angularconfiguration of the optical axes, and that of the polarizers of theglasses 105, etc. may be suitably deviated from the conditions asdescribed so far for an optimum design.

The ferroelectric smectic liquid crystal cell is very suitable for theembodiment of the present invention. More specifically, there arevarious superior characteristics which cannot be available from otherliquid crystal cells such that it can sufficiently withstand a highspeed response at several tens to several hundred microseconds, that thedirections of optical axes move only within the plane of the liquidcrystal cell 103, and further, that a memory effect is present in theswitching state, etc.

Hereinbelow, principles of functioning of the above ferroelectricsmectic liquid crystal cell will be described.

This light switching element utilizing the chiral smectic liquid crystalshowing ferroelectric characteristics was published in "Applied PhysicsLetters" (Vol. 36, page 899, published in 1980) by N. A. Clark and S. T.Lagerwall, and is named as "Surface-Stabilized Ferroelectric LiquidCrystal". FIG. 4(A) shows a cross section of the above liquid crystalcell when an electric field is applied thereto, which includes glasssubstrates 107, respectively provided at the inner faces thereof, withtransparent electrodes 108, between which liquid crystal molecules 109are accommodated, with the electric field within the cell being directedfrom the upper portion to the lower portion in the drawing. With respectto the above electric field, dipoles of the liquid crystal molecules 109are aligned as indicated by the arrows. In the diagram of FIG. 4(B)showing the molecular alignment under the above state as viewed in adirection perpendicular to the cell surface, each of liquid crystalmolecules 109 has its long axis inclined by an angle θ with respect to aline normal to the plane of the alignment lattice, i.e., layer.Subsequently, upon inversion of the polarity of the applied electricfield, the dipoles of the liquid crystal molecules 109 are inverted asindicated by the arrows in FIG. 5(A), and each of the liquid crystalmolecules 109 changes its azimuth in a direction of an angle -θ as inFIG. 5(B).

For a practical application purpose, the above liquid crystal cell maybe considered, in terms of optical crystallography, to be of an uniaxialcrystal having an aligning direction of the molecule long axis as theoptical axis. In other words, this liquid crystal cell may be regardedas an optical compensator capable of rotating the optical axis by anangle 2θ through inversion of the polarity of the applied voltage. It isto be noted that the rotation of this optical axis is symmetrical aroundthe normal line with respect to the smectic layer, and that theretardation of this liquid crystal cell may be represented by a productof the birefringence Δn of the liquid crystal and the thickness d of thecell (Δn·d).

Although the tilt angle θ of the liquid crystal molecule 109 differsaccording to liquid crystal materials, it is preferable that 2θ is of90° for application to the first system as described earlier, andtherefore, a material with the angle θ of 45° is suitable. While for theapplication to the second and third systems also referred to earlier, amaterial having the angle θ of 22.5° is suitable, since 2θ shouldpreferably be 45°. However, for the practical application, deviation ofthe angle θ by approximately ±10° from the above conditions ispermissible.

The liquid crystal cell as described above shows a memory effect in theon/off switching state. More specifically, as shown in FIG. 6, even whenthe applied voltage is reduced to 0V after switching by an electricfield in the form of pulses in positive and negative polarities, therespective states of molecular alignment are generally maintained.According to the literature referred to earlier, the response time τ ofthis liquid crystal cell is represented by a formula,

    τ∝η/(Ps·E)

where η represents the viscosity of the liquid crystal material, Psshows spontaneous polarization thereof,

and E denotes the intensity of the electric field,

and for effecting a higher speed switching, a stronger electric field ismore advantageous. Various waveforms may be considered for the voltageto be applied to this liquid crystal cell as long as the voltage caneffect a faster switching-over speed of the liquid crystal cell thanthat of the television images, and as the phases of the voltage areproperly controlled so that the images may be correctly sent to the leftand right eyes. The simplest waveform is a square wave.

Furthermore, if it is intended to save power consumption and obtain longlife of the liquid crystal cell through utilization of the memoryeffect, the waveform as shown in FIG. 7 may be employed, which is soarranged that a high speed switching is effected at voltages having highwave height values such as in the period t₁₀₁ or t₁₀₃, and in theperiods t₁₀₂ and t₁₀₄ thereafter. Voltages necessary to maintain themolecular alignment as it is, through utilization of the memory effect,are applied. Moreover, it may be so arranged to superpose a DC offsetvoltage on the applied voltage waveform in order to improve theretaining characteristics of the memory effect.

As described so far, since the stereographic display system of themultiplexed double image type according to the first embodiment of thepresent invention has such advantages that the construction is simple,and moreover, the glasses to be worn by the viewers are light andinexpensive, this system may be readily utilized at homes in general, inclassrooms, etc., thereby being very suitable for actual applications.

[SECOND EMBODIMENT]

The virtual stereographic display system according to a secondembodiment of the present invention is also characterized in that thestereographic image display is effected in such a manner that, with theliquid crystal cell disposed before the television image surface onwhich the images for the left eye and right eye are alternatelydisplayed by time division. The polarization axis of light travellingthrough said liquid crystal cell is alternately switched over by thetime division for observation by glasses with polarizing plates throughseparation into left and right eyes, and thus, the stereographic imagedisplay is executed based on the parallax of the respective imagesproduced between after-images in the left eye and right eye.

Referring to FIG. 8, there is shown a virtual stereographic imagedisplay system V2 according to the second embodiment of the presentinvention. This system generally includes the image display surface 101similar to that in the first embodiment of FIG. 1, a guest-host typeliquid crystal cell 110 (referred to as a GH liquid crystal cellhereinafter) disposed before the image display surface 110, and aquarter-wave plate 106 further disposed before the GH liquid crystalcell 110 for converting the plane or linearly polarized light travellingthrough the liquid crystal cell 110 into the generally circularlypolarized light 207. The driving circuit 104 for driving the liquidcrystal cell 110 is connected between the television set and said liquidcrystal cell in a similar manner as in the first embodiment.

The GH liquid crystal cell 110 is prepared through homogeneous alignmentof a mixed ferroelectric smectic liquid crystal added with a blackdichroic dye, and provided with transparent electrodes (not particularlyshown) at the inner sides of its substrates for application of anelectric field to the mixed liquid crystal. The light travelling throughthe GH liquid crystal cell 110 becomes the plane-polarized light, whosepolarization axis may be altered by approximately 90° throughswitching-over of the voltage applied to the GH liquid crystal cell 110.The driving circuit 104 for the GH liquid crystal cell 110 is intendedto form the voltage waveform to be applied to the GH liquid crystal cell110, and arranged to alternately switch-over the optical axis of the GHliquid crystal cell 110 in synchronization with the frame signal of thetelevision signal fed from the television set T. The glasses 105provided for the viewer to wear are equipped with circularly polarizingplates having opposite polarization axes respectively for left and righteyes as referred to earlier.

For setting the optical axis for the quarter-wave plate 106, it shouldpreferably be so arranged as shown in FIG. 9 that, in order to equalizethe amount of light reaching the left and right eyes of the viewer asfar as possible, the symmetry axis 210 (i.e., a normal line of thesmectic layer) of the two optical axes 202 and 203 which can be taken bythe GH liquid crystal cell 110, is approximately aligned with theoptical axis 206 of the quarter-wave plate 106.

The prevention of the quarter-wave plate 106 before the liquid crystalcell 110 and the circular polarizing plates on the glasses 105, preventsany adverse effect to the separation of the images for the left andright eyes, even when the viewer inclines his head to the left or right.If such consideration is not particularly required, plane or linearpolarizing plates may be attached to the glasses 105 as shown in amodification V2B of FIG. 10. In this modified system V2B, the setting ofthe two polarization axes 208 and 209 which can be taken by the GHliquid crystal cell 110 and the polarization axes 204 and 205 of thepolarizing plates attached to the glasses 105 should be so arranged asshown in FIG. 11, so that one polarization axis 204 of the glassesintersects at right angles with one polarization axis 209 which can betaken by the GH liquid crystal cell 110, while the other polarizationaxis 205 also intersects at right angles with the other polarizationaxis 208 which may be taken by the G liquid crystal cell.

The ferroelectric smectic liquid crystal cell is also very suitable forthis embodiment of the present invention. As referred to earlier, thereare various superior characteristics which cannot be made available fromother liquid crystal cells such that it can sufficiently withstand ahigh speed response at several tens to several hundred microseconds, andthat the directions of optical axes move only within the plane of the GHliquid crystal cell 110, and further, that the memory effect is presentin the switching state, etc.

Hereinbelow, principles of functioning of the above guest-host typeferroelastic smectic liquid crystal cell will be described.

As also referred to earlier, this light switching element utilizing thechiral smectic liquid crystal showing ferroelectric characteristics waspublished in "Applied Physics Letters" (Vol. 36, page 899, published in1980) by N. A. Clark and S. T. Lagerwall, and is entitled"Surface-Stabilized Ferroelectric Liquid Crystal". Here, liquid crystalis mixed with the dichroic dye, and is applied to the present inventionas will be explained.

FIG. 12(A) shows a cross section of the above liquid crystal cell whenan electric field is applied thereto, which includes glass substrates107, respectively provided at the inner faces thereof, with transparentelectrodes 108, between which liquid crystal molecules 109 areaccommodated, with molecules of the dichroic dye and external lightbeing designated by numerals 111 and 212 respectively. In this liquidcrystal cell, the electric field is directed from the upper portion tothe lower portion in the drawing. With respect to the electric field ofabove, dipoles of the liquid crystal molecules 109 are aligned asindicated by arrows. In the diagram of FIG. 12(B) showing the molecularalignment under the above state as viewed in direction perpendicular tothe cell surface, each of liquid crystal molecules 109 has its long axisinclined by an angle θ with respect to a line perpendicular to the planeof the alignment lattice, i.e., layer, with the dichroic dye molecules111 being also inclined generally in the same direction. In the lighttravelling through the liquid crystal cell under the above state, apolarization component 213 in the long axis direction of the molecule ofthe dichroic dye 111 is absorbed by the cell, while another polarizationcomponent 214 intersecting at right angles therewith is allowed to passtherethrough. Consequently, the transmitting light becomes a plane orlinearly polarized light 211 having 90°-θ as an axis.

Subsequently, upon inversion of the polarity of the applied electricfield, the dipoles of the liquid crystal molecules 109 are inverted asindicated by the arrows in FIG. 13(A). Each of the liquid crystalmolecules 109 changes its azimuth in a direction of an angle -θ. Sincethe molecules 111 of the dichroic dye incline in the same direction, thelight transmitting through the liquid crystal cell 110 becomes theplane-polarized light 211 having 90°+θ as an axis.

As described above, this GH liquid crystal cell 110 may be regarded as apolarizer capable of rotating the optical axis by an angle 2θ through aninversion of the polarity of the applied voltage.

Although the tilt angle θ of the liquid crystal molecule 109 differsaccording to liquid crystal materials, it is preferable that 2θ is of90° for application to the first system as described earlier, andtherefore, a material with the angle θ of 45° is suitable.

The liquid crystal cell as described above shows a memory effect in theon/off switching state. More specifically, as also described earlierwith reference to FIG. 6, even when the applied voltage is reduced to 0Vafter switching by an electric field in the form of pulses in positiveand negative polarities, the respective states of molecular alignmentare generally maintained. According to the literature referred toearlier, the response time τ of this liquid crystal cell is representedin a similar manner as referred to earlier by a formula,

    τ∝η/(Ps·E)

where η represents the viscosity of the liquid crystal material, Psshows the spontaneous polarization thereof,

and E denotes the intensity of electric field,

and for effecting a higher speed switching, a stronger electric field ismore advantageous. Various waveform may be considered for the voltage tobe applied to this liquid crystal cell as long as the voltage can causea faster switching-over speed of the liquid crystal cell than that ofthe television images, and as the phases of the voltage is properlycontrolled so that the images may be correctly sent to the left andright eyes. The simplest one of waveforms is a square wave.

Furthermore, if it is intended to save power consumption and produce along life of the liquid crystal cell through utilization of the memoryeffect, the waveform as shown in FIG. 7 may be employed. The waveform isso arranged that the high speed switching is effected at voltages havinghigh wave height values such as in the period t₁₀₁ or t₁₀₃, and in theperiods t₁₀₂ and t₁₀₄ thereafter, voltages necessary to maintain themolecular alignment as it is, through utilization of the memory effect,are applied. Moreover, it may be so arranged to superpose the DC offsetvoltage on the applied voltage wavefrom in order to improve theretaining characteristics of the memory effect.

As described so far, the stereographic display system of the multiplexeddouble image type according to the second embodiment of the presentinvention has such advantages that the construction is simple, and thatthe glasses to be worn by the viewers are light and inexpensive. Saidsystem may also be readily utilized at homes in general, in classrooms,etc., and for actual applications.

[THIRD EMBODIMENT]

The virtual stereographic display system according to a third embodimentof the present invention is characterized in that the stereographicimage display is effected in such a manner that, the images for the lefteye and right eye are alternately displayed on the television imagedisplay surface through change-over by time division, and such imagesare observed separately by the left and right eyes by the glasses withlight valves.

In FIG. 14, there is shown a general construction of a virtualstereographic image display system V3 according to the third embodimentof the present invention. The system generally includes the imagedisplay surface 101 of a display unit such as a television set T or thelike, and glasses 105Q for a viewer to wear provided with transientscattering mode liquid crystal cells 113 (referred to as TSM liquidcrystal cell hereinafter) respectively for the left and right eyes, withthe driving circuit 104 being connected between the television set T andthe liquid crystal cells 113. Here, the term "television" means, asstated earlier, the arrangement adapted to transmit images as convertedinto electrical signals via passages through a wire or wireless systemfor reproduction of the images by a receiving set. The display device tobe used therefor, may be a CRT (cathode ray tube), liquid crystaldisplay unit, electro-luminescence display, light emitting diode matrixdisplay, plasma display and screen of a projecting type television, etc.Each of the TSM liquid crystal cells 113 has the ferroelectric smecticliquid crystal molecules 109 enclosed therein, and is provided with thetransparent electrode 108 at the inner side of each of the glasssubstrates 107 as shown in FIG. 15. In the present embodiment, each ofthe TSM liquid crystal cells 113 functions as an electronic light valvethorugh control of the voltage applied to the transparent electrodes108. The driving circuit 104 for the TSM liquid crystal cell 113 isintended to form the voltage waveforms to be applied to the TSM liquidcrystal cells 113, and is arranged to alternately switch over the leftand right TSM liquid crystal cells 113 into a transparent state orscattering state.

As the device for displaying the images, display systems based onprojection of photographs and films are similarly utilized besides theelectrical display devices such as the television set and the like. Inthis case, it is only required to replace the image display surface by areflective or transmissive type screen, and for other appliances, thesame ones as those employed in the system of FIG. 14 may be employed.

The transient scattering mode, i.e., TSM ferroelectric smectic liquidcrystal cell is very suitable for the purpose of the present invention.More specifically, since the response speed is high at several tens toseveral hundred microseconds, the liquid crystal cell can fully copewith the frame frequency at several ten Hz, and moreover, since it is ofthe scattering type, variation in the transmitted light amount due tothe opening or closing of the light valves is not excessive, with aconsequent of less eye fatigue. Such characteristics as described abovecannot be noticed in the other liquid crystal cells.

Subsequently, functioning principles of this ferroelectric smecticliquid crystal cell will be explained.

This light switching element utilizing the chiral smectic liquid crystalshowing the ferroelectric characteristic is published in "JapaneseJournal of Applied Physics" (Vol. 23, page L385, published in 1984) byK. Yoshino et al., and is named as "Transient Scattering Mode (i.e.,TSM) Liquid Crystal". The TSM liquid crystal cell has the cross sectionas described earlier with reference to FIG. 15, and employs nopolarizer.

Hereinbelow, electro-optical effects of this liquid crystal cell will beexplained.

FIG. 16(A) shows the state where a DC voltage is applied to said liquidcrystal cell. With respect to this electric field, since dipoles of theliquid crystal molecules 109 are aligned as indicated by the arrows, theliquid crystal molecules 109 are aligned in parallel relation withrespect to the substrates 107. In this state, the liquid crystal cell istransparent.

Subsequently, upon inversion of the polarity of the applied electricfield, dipoles of the liquid crystal molecules 109 are inverted asshown, and the liquid crystal molecules 109 change the direction thereofso as to be re-aligned in parallel with respect to the substrates 107.In this state also, the liquid crystal cell still remains transparent(FIG. 16(C)). Meanwhile, in the transient state in which there-alignment of molecules in the inverting process is taking place,light 212 incident upon the cell is scattered as shown at 216 in FIG.16(B) (the transmitting light is represented by numeral 215). When thepolarity of the applied voltage is further inverted, the cell resumesthe tranparent state in FIG. 16(A) after the transient scattered stateas shown in FIG. 16 (D).

FIG. 17 shows the relation between the applied voltage waveform and thescattering light intensity. From the diagram in FIG. 17, it is seen thatthe scattering is started immediately after the polarity of the appliedvoltage is inverted from the positive polarity to the negative polarityand also from the negative polarity to the positive polarity, and aftercontinuation of the scattering state at a certain time period, the cellagain resumes the transparent state. In order to maintain the scatteringstate for a long time, an AC voltage for a short period may be applied.

For the purpose of driving the liquid crystal cell having the abovecharacteristics as applied to the display system of the presentinvention, a waveform as shown in FIG. 18 is suitable. Morespecifically, in FIG. 18, the liquid crystal cell is brought into thetransparent state through application of DC voltage at periods t₁₁₁ andt₁₁₃, and into the scattering state through application of AC voltage atperiods t₁₁₂ and t₁₁₄. By rotatively repeating such four periods, thetransparent state and the scattering state are caused to alternatelytake place. Here, it is so arranged that the time for each of theperiods from t₁₁₁ to t₁₁₄ is made equal to the display time for oneframe, with the polarity of voltage at the periods t₁₁₁ and t₁₁₃ beingadapted to be reversed in the positive and negative polarities.

Generally, for driving a liquid crystal cell, it is necessary to removea DC component from the driving waveform in order to preventdeterioration of the liquid crystal by electrolysis. In this respect,the driving waveform as shown in FIG. 18 presents no particularproblems, because the maximum period during which the DC voltage isapplied is a short time equivalent to one frame time, and no DCcomponent is contained upon time-averaging.

Since the stereographic display system of multiplexed double image typehas the advantage in that viewers' eyes are not readily tired, it issuitable to use for a long period of time. Moreover, since the use oftelevision sets and film projection apparatuses at home have widelyspread in general, etc., the present invention may be readily effectedfor wide applications.

[FOURTH EMBODIMENT]

The virtual stereographic display system according to a fourthembodiment of the present invention is based on the arrangement that theimages for the left eye and right eye are alternately displayed on thetelevision image display surface so as to observe the light signals ofthe images through the employment of means having a light valve functionand driven by a voltage in a waveform synchronized with the frame signalof the images, and characterized in that the signal synchronized withthe frame signal is formed by the output signal of a photosensor fordetecting brightness variations on the image display surface. Also, asignal different in brightness according to the image for the right eyeor the image for the left eye is displayed at a predetermined sameregion of the image for the right eye as the image for the left eye. Thesignal is judged on whether it is for forming an image for the right eyeor for the left eye by the brightness variation signal as detected bysaid photosensor.

Referring to FIG. 19, there is shown a virtual stereographic displaysystem V4 according to the fourth embodiment of the present invention.The system includes the image display surface 101 of a display devicesuch as a television set T or the like, a photosensor 114 disposed in aposition capable of detecting brightness variation in a predeterminednarrow region of the image display surface 101, a synchronizing signalgeneration circuit 115 connected to the output end of the photosensor114 so as to form the frame signal of display from the output of saidphotosensor 114, and a driving circuit 116 for driving the light valves117 of the glasses 105V to be worn by the viewer, with said drivingcircuit 116 being connected to the synchronizing signal generationcircuit 115 by a wire or a wireless system (not shown).

In the embodiment of FIG. 19, the photosensor 114 detects the images forthe left eye and right eye to be displayed on the image display surface101 by the brightness variation, and thus, the light valves 117 for therespective left and right eyes are alternately opened or closedaccording to the frame signal produced by the photosensor 114 and thesynchronizing signal generation circuit 115. Therefore, the images forthe left eye and the right eye that are to be alternately displayed onthe image display surface 101 are respectively separated to the left eyeand the right eye of the viewer, and thus, both of the images deviatedfrom each other are observed as composed, thereby providing thestereoscopic view.

In a modified display system V4B in FIG. 20, a polarization controlpanel 118 is further disposed before the image display surface 101, andthe driver 116 connected to the synchronizing signal generating circuit115 coupled to the photosensor 114, is connected to said polarizationcontrol panel 118, with the glasses 105V with the light valves 117 beingreplaced by the glasses 105 having polarizing plates P with differentpolarization axes for the left and right eye.

In the display system V4B, the viewer observes the images on the displaysurface 101 travelling through the polarization control panel 118 by theglasses 105, in which the images are viewed alternately for the left andright eyes by the polarizing plates P of the glasses 105 at the sidecoincident with the polarization axis alternately changed over by thecontrol panel 118. The output signal of the photosensor 114 whichdetects the brightness variation at the predetermined small region onthe image display surface 101, is converted into the frame signal by thesynchronizing signal generating circuit 115, and in synchronization withthis signal, the polarization control panel 118 is driven by the driver116. More specifically, the polarization axis of the polarizationcontrol panel 118 is changed over for each frame signal, and light ofthe images displayed on the image display surface 101 becomes the planeor circularly polarized light after travelling through the polarizationcontrol panel 118. On the image display surface 101, the image for theleft eye and the image for the right eye are alternately displayed, andthe polarization axis of the polarization control panel 118 is so setthat polarization axes of light of the image for the left eye and thatfor the right eye intersect at a right angle with each other aftertravelling through said control panel 118. When the light travellingthrough the polarization control panel 118 is observed by the viewerwearing the glasses 105 provided with the two plane or circularlypolarizing plates P at the left and right sides, whose polarization axesintersect each other, the images for the left eye and right eye arerespectively separated into the left eye and right eye, and thus, thestereoscopic view may be obtained based on the parallax of both images.

The apparatus for displaying images may be any one so long as it canimpart light at an intensity exceeding the sensitivity of thephotosensor 114 to said photosensor 114. For example, besides televisionsets employing the cathode ray tube or liquid crystal display, a filmprojecting apparatus may also be employed. In the case where a filmprojector is used, the photosensor may be disposed near the screen or atleast at part of a light path in the projector.

Subsequently, the process for generating the synchronizing signal willbe explained by taking up the television as one example.

When light at a certain predetermined portion of the image displaysurface 101 of the cathode ray tube for the television set is detectedby a photosensor 114 such as a CdS cell, photodiode, photo-transistor orthe like, a waveform as shown in FIG. 21(A) is obtained. This waveformis first converted into a square waveform as shown in FIG. 21(B). In anordinary television apparatus, the system to effect the scanning at twofields for displaying one frame of picture, i.e., the so-called 2:1interlace scanning is effected. Accordingly, since the waveform in FIG.21(B) is equal to the frequency of the field scanning, if this issubjected to frequency division to 1/2, a waveform with the samefrequency as the driving frequency of the light valves may be obtained.In this case, the frequency division must be effected at a correct phaserelation so that the field scanning in two times for the same framecorresponds to the same frame of the frequency divided waveform.Moreover, if the distinction between the left eye image and right eyeimage is adapted to correspond to the voltage level of the frame signal,the frequency division should be effected so as to make this phaserelation also correct.

More specifically, phases applicable to the frequency division of thewaveform in FIG. 21(B) are available in four kinds as represented inFIGS. 21(C) to 21(F), and the viewer can notice the stereoscopic view byonly one kind of the above. The simplest way to select the correct phaseis to have the viewer himself select the phase so that he can feel thecorrect stereoscopic view. For other methods, a practice may beconceived to display the phase control signal as part of the imagedisplay surface 101. This is the method in which the image informationis not displayed at the certain predetermined regions of the imagedisplay surface 101, and some information of brightness variationcorresponding to the distinction between the left eye image and righteye image is displayed at said region, thereby selecting the brightnessphase by the difference as detected by the photosensor. By this method,the phase selection may be completely automated.

Accurate correction is also required for a delicate phase deviation ofthe frame. Since this mainly depends on the position of light on theimage display surface as detected by the photosensor, if the photosensoris properly set and the phase of the frame is finely adjusted, there isnot a necessity for any re-adjustments thereafter.

As is seen from the foregoing description, according to the aboveembodiment of the present invention, the synchronizing signal fordriving the light valves may be obtained by only disposing thephotosensor near the image display surface of an existing televisionset, with employment of inexpensive circuits. Therefore, a very usefultechnique for readily enjoying spectacular stereoscopic images at home,etc. can be advantageously presented.

[FIFTH EMBODIMENT]

The virtual stereographic display system according to a fifth embodimentof the present invention includes a television display surface on whichimages for the right eye and left eye are alternately displayed.Observation glasses for observing light signals of said images areprovided with a pair of light valves to be opened or closed in turn insynchronization with the cycle for switching over the images for theright eye and the left eye, and is characterized in that the unit forswitching-over the two kinds of image information for the right and lefteyes is constituted by one scanning line or a group of a predeterminedplurality of scanning lines.

As also referred to earlier, the term "television" used here relates tothe arrangement adapted to transmit images as converted into electricalsignals via passages through a wire or wireless system for reproductionof the images by a receiving set. As the display device to be usedtherefor, there may be raised the CRT (cathode ray tube), liquid crystaldisplay unit, electro-luminescence display, light emitting diode matrixdisplay, plasma display and screen of a projecting type television, etc.According to the present embodiment, however, the arrangement is limitedto that in which the means for constituting the images employs scanninglines.

It is to be noted here that, according to the present invention, theopen/close cycle of the light valves is of a high speed at 15.75 KHz,e.g. In the NTSC system, the present inventors have completed thepresent invention by making it possible to effect the open/closefunction at such a high speed through utilization of, for example, thebirefringence effect of the ferroelectric liquid crystal for lightvalves. However, the light valves to be employed in the presentinvention are not limited to those which employ the ferroelectric liquidcrystal.

More specifically, in the present embodiment, the repetition unit foralternately displaying the image information for the left eye and theright eye is altered from the conventional frame or field to thescanning line which may be switched over at a higher speed forelimination of the undesirable flickering. Since the repeating frequencyof the scanning line is at 15.75 KHz in the NTSC system as referred toabove, and is by far at a higher speed than 30 Hz or 60 Hz for the frameor field frequency, the flickering is not noticeable by viewers.

Referring to FIGS. 22 and 23, principle for the fifth embodiment of thepresent invention will be explained.

In FIGS. 22(A), 22(B) and 22(C), there are shown scanning lines in oneframe of a non-interlace system for a television set employing a cathoderay tube.

As shown in FIG. 22(A), for example, the image information for the righteye is displayed on the odd-numbered scanning lines, while the imageinformation for the left eye is displayed on the even-numbered scanninglines. When the image display surface in FIG. 22(A) is viewed withoutwearing the glasses 105V with the light valves referred to earlier (FIG.19), the images for the left eye and the right eye appear to beperfectly overlapped with each other. Meanwhile, if the above images areobserved through the glasses 105V with the light valves which arealternately opened or closed for the left and right eyes for eachhorizontal period in synchronization with the horizontal synchronizingsignal, the image for the right eye constituted only by the odd-numberedscanning lines as shown in FIG. 22(B) and the image for the left eyeconstituted only by the even-numbered scanning lines as shown in FIG.22(C) are discriminated from each other for arrival at the right andleft eye respectively.

FIGS. 23(A) to 23(E) are diagrams showing the synchronizing relationbetween the television signals and the open/close function of the lightvalves for the observation glasses. In FIG. 23(A) representing thetelevision signal, symbols Hi, Hi+1, . . . and Hi+6 respectively showthe horizontal signal periods at ith ,i+1st . . . and i+6th. In FIG.23(B), there is shown the open/close function at one side of the glasses105V with the light valves, for example, the open/close function of thelight valve 117a for the right eye in a graphical form (FIG. 24), whichis driven so as to be actuated in synchronization with the horizontalsynchronizing signal. When the image display surface 101 is observedthrough the light valve 117a, the image information on the scanninglines at Hi+1, Hi+3, and Hi+5 reaches the right eye as shown in FIG.23(C). The other light valve 117b of the glasses 105 is driven so as toeffect the open/close function in the phase relation as shown in FIG.23(D). Upon observation of the image display surface through this lightvalve 117b, the image information on the scanning lines at Hi, Hi+2,Hi+4 and Hi+6 reaches the left eye as shown in FIG. 23(E).

Referring also to FIG. 24, there is shown the construction of a virtualstereographic display system V5 according to the fifth embodiment of thepresent invention related to a television system of non-interlace type.

On the image display surface 101 of a television set T including acathode ray tube or the like, the image information for the right eyeand the left eye is alternately displayed per each horizontal scanning.

The observation glasses 105V' include the light valve 117a for the righteye and the light valve 117b for the left eye which are respectivelyconnected to the driving circuit 116 and further coupled to thetelevision set T through the synchronizing signal generating circuit 115so as to be alternately opened or closed by the driving signal suppliedfrom the driving circuit 116. The circuits 116 and 115 are coupled toeach other through a wire or wireless system. For the functioning signalof the driving circuit 116, a signal obtained through shaping of thehorizontal synchronizing signal by the circuit 115 is employed. By theabove arrangement, the glasses 105V' having the light valves 117a and117b are adapted to be opened, at one side thereof, only during thehorizontal scanning period of the image display surface, with the otherside thereof being closed, and such function is arranged to bealternately repeated.

For the respective light valves 117a and 117b, the ferroelectric smecticliquid crystal cells are employed. More specifically, each of the lightvalves 117a and 117b include a cell having a pair of substrates eachprovided with a transparent electrode at its inner side, between whichthe ferroelectric smectic liquid crystal is enclosed for homogenousalignment, with polarizing plates being disposed on the opposing outersurfaces of the cell.

In the present embodiment, the response speed required for the glasses105V' with the light valves and related to a horizontal retrace period,is about 11 microseconds, and the ferroelectric smectic liquid crystalcell is extremely suitable for the glasses 105V' having suchrequirements. In other words, the ferroelectric liquid crystal cell iscapable of effecting the switching through high speed response asdescribed above at the applied voltage of ten to several ten volts, andreadily provides contrast and transmittance required for the lightvalves. Such features cannot be available in other liquid crystal cells.The driving circuit 116 is a circuit to produce the voltage waveform tobe applied to such liquid crystal cell.

Subsequently, referring back to the diagram for explaining the scanninglines on the image display surface 101 in FIGS. 22(A) to 22(C), and thediagram for explaining the synchronizing relation between the televisionsignal and the open/close function of the glasses with the light valvesin FIGS. 23(A) to 23(E), the function of the display system V5 in FIG.24 will be explained more specifically.

On the image display surface 101 of the non-interlace system, forexample, the image information for the right eye is displayed on theodd-numbered scanning lines represented by solid lines, while the imageinformation for the left eye is displayed on the even-numbered scanninglines represented by dotted lines as shown in FIG. 22(A).

As state earlier, FIG. 23(A) denotes the television signal, and symbolsHi, Hi+1, . . . and Hi+6 respectively show the horizontal signal periodsat ith, i+1st, . . . and i+6th.

When the image display surface 101 as described above is observedthrough the light valve 117a to be opened or closed at periods as shownin FIG. 23(B), only the image information on the scanning lines at Hi+1,Hi+3 . . . , etc. reaches the right eye. In other words, the imageconstituted only by the odd-numbered scanning lines is observed by thrright eye as shown in FIG. 22 (B). Similarly, through the light valve117b for the left eye having the open/close function as represented byFIG. 23(D), the image information on the scanning lines at Hi, Hi+2, . .. , etc. is to reach the left eye, and thus, the image constituted onlyby the even-numbered scanning lines is observed by the left eye as shownin FIG. 22(C).

As referred to earlier also, in the NTSC system, since the repeatingfrequency of the scanning lines is 15.75 KHz, which is by far a higherspeed than in the case where the image information is changed over atthe conventional frame or field frequency of 30 Hz or 60 Hz, noflickering is noticed at all.

Subsequently, one example of experiments carried out by the presentinventors with respect to the case where the interlace system isemployed will be described.

Through employment of a computer graphic image system with the number ofscanning lines of 400, still images both for the left eye and right eyewere displayed on a cathode ray tube of the interlace system. In theabove case, image data were so prepared that on the scanning linenumbers 1, 2, 5, 6, . . . 4i+1, 4i+2, 4i+5, 4i+6, . . . 393, 394, 397and 398, the image for the right eye is displayed, while on the scanningline numbers 3, 4, 7, 8, . . . 4i+3, 4i+4, 4i+7, 4i+8, . . . 395, 396,399 and 400, the image for the left eye is displayed. By the abovearrangement, in the odd-numbered fields, the scanning lines 1, 5, 9, 13,. . . 4i+1, . . . 397, displaying the image information for the righteye and the scanning lines 3, 7, 11, . . . 4i+3, . . . 399, displayingthe image information for the left eye are displayed. Meanwhile, in theeven-numbered fields, the scanning lines 2, 6, . . . 4i+2, . . . 398,displaying the image information for the right eye and the scanninglines 4, 8, . . . 4i+4, . . . 400 displaying the image information forthe left eye are displayed. When the above images were observed throughthe glasses having the light valves of ferroelectric smectic liquidcrystal cells driven by a square wave at 25 V, 15.75 KHz synchronizedwith the horizontal synchronizing signal, stereoscopic images completelyfree from flickering could be observed.

As is clear from the foregoing description, according to the fifthembodiment of the present invention, in the virtual stereographicdisplay system of the multiplexed double image system, since it is soarranged that the change-over of the multiplexed double imageinformation is adapted to be effected per one or a plurality ofhorizontal scannings, the period of the change-over occurs at a highspeed of 15.75 KHz in the change-over per each horizontal scanning, forexample, in the NTSC system, and thus, no flickering is felt by theviewers and eye fatigue does not result. Furthermore, since it is notrequired to change the frame frequency or field frequency of theexisting television set, the present invention can be readily put intoactual application.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to be notedhere that various changes and modifications will be apparent to thoseskilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention, theyshould be construed as being included therein.

What is claimed is:
 1. A virtual stereographic display system forsupplying a stereographic image to an observer, comprising:display meansfor alternately displaying right eye information and left eyeinformation by interleaving said display means with a first set ofscanning lines containing right eye information and with a second set ofscanning lines containing left eye information; synchronizing signalgenerating means for developing synchronizing signals in response to atransition between said right eye information and said left eyeinformation supplied said display means from said first set of scanninglines and said second set of scanning lines, and optical means forallowing the right eye of the observer to view only said right eyeinformation and the left eye of the observer to view only said left eyeinformation, said optical means including right and left eye valve meansfor selectively transmitting said right eye information and said lefteye information to the right and left eyes of the observer, said opticalmeans switching said right eye valve means substantially transmissivewhile switching said left eye valve means substantially opaque, andswitching said left eye valve means substantially transmissive whileswitching said right eye valve means substantially opaque in reponse tosaid synchronizing signals.
 2. A virtual stereographic display system ofclaim 1, wherein said right and left eye valve means respectivelycomprise a right eye polarizing plate and a left eye polarizing platehaving different polarization axes, said optical means furthercomprising a polarization control panel placed before said display meansand selectively transmitting polarized light of different polarizationaxes from said display means in response to said synchronizing signals.3. A virtual stereographic display system of claim 1, wherein said rightand left eye valve means each include a cell of transient scatteringmode liquid crystal being aligned or scattered in response to saidsynchronizing signals thereby selectively switching said right and lefteye valve means substantially transmissive and substantially opaque. 4.A virtual stereographic display system of claim 3, wherein said cell isof a ferroelectric smectic liquid crystal.
 5. A virtual stereographicdisplay system of claim 1, wherein said synchronizing signal generatingmeans comprises photosensor means for detecting brightness variations ofsaid display means, said synchronizing signal generating meansdeveloping said synchronizing signals in response to an output of saidphotosensor means.
 6. A virtual stereographic display system of claim 5,wherein said photosensor means detects brightness variations from apredetermined region of said display means.
 7. A virtual stereographicdisplay system of claim 5, wherein said photosensor means is a CdS cell.8. A virtual stereographic display system of claim 5, wherein saidphotosensor means is a photodiode.
 9. A virtual stereographic displaysystem of claim 5, wherein said photosensor is a phototransistor.